1. Field of the Invention
The present invention relates to an information communication terminal, a radio communication apparatus and a radio communication network system, and particularly to an information communication terminal, a radio communication apparatus and a radio communication network system that can perform a communication corresponding to a purpose.
2. Description of the Background Art
In recent years, radio communications performed between a plurality of information communication terminals without using an access point are becoming widely available. The network that is formed of only terminals capable of such radio communications is called “ad hoc network”.
Various techniques relating to terminals that can perform communications over the ad hoc network have been disclosed. For example, a patent document 1 (Japanese Patent Laying-Open No. 2000-115012) has disclosed a portable communication apparatus that can easily exchange data between an indefinite number of apparatuses.
Further, a patent document 2 (Japanese Patent Laying-Open No. H03-267844) has disclosed a technique in which a redundant code called “FCS (Frame Check Sequence)” is added to each frame, and a receiver performs error check on each frame by checking the redundant code.
In the above patent document 1, each portable communication apparatus basically repeats transmission of its own message at intervals of five seconds for allowing mutual transmission of messages between the indefinite number of apparatuses. When a power saving mode (operation mode having a long transmission interval) or a sleep mode (pause) is detected while the above message transmission is being repeated, the apparatus enters the power saving mode or the sleep mode. In these modes, the transmission intervals are long, either the transmission or reception stops, a transmission radio wave is weak or an intermittent operation is performed. However, these modes are selected according to conditions relating to whether the reception occurs within a predetermined time or not, and this document has not disclosed a technique for entering the power saving mode or the sleep mode according to a length of a standby period for the reception.
In the ad hoc network using a wireless (radio) LAN (Local Area Network), each terminal is required to have small power consumption because it is of a portable type. As described above, however, the conventional apparatus is merely configured to enter always a standby state for the reception, or to enter the sleep mode or the power saving mode when it does not receive the data over a predetermined period, and measures for reducing the power consumption more finely have not been proposed.
In some cases, it is desired to transmit, e.g., reproducible uncompressed A/V data (Audio-Visual data) to a terminal on the other end of communications without error check even when data corruption may occur to a certain extent. Even in these cases, an error frame having corrupted data is abandoned on a reception side because the transmission over the conventional LAN is configured to perform always FCS error check (i.e., error check performed on each frame by checking a redundant code indicated by the FCS) is performed on a frame-by-frame basis. Consequently, the A/V data stored in the abandoned frame is not received, and therefore data dropout occurs on the reception side, resulting in a problem that a sound is not continuously reproduced on the reception side when the transmitted data is audio data.
This will be described below with reference to FIG. 46. FIG. 46 schematically shows a conventional communication sequence for performing the FCS error check on the ad hoc network. In FIG. 46, the transmitting-side terminal is formed of a host system and a communication circuit, and a receiving-side terminal is likewise formed of a communication circuit and a host system. Each terminal performs mutual communications between the host system and the communication circuit.
Referring to FIG. 46, on the transmitting-side terminal, a first data transmission request provided from the host system is transmitted as a first frame via the communication circuit to the network.
When the communication circuit in the receiving-side terminal receives the first frame, it performs the FCS check. When it is determined that there is no error (OK), it provides the received first data to the host system, produces a frame of ACK (ACKnowledgement) and transmits it to the network.
Subsequently, the transmitting-side terminal transmits a second frame storing second data to the receiving-side terminal.
On the receiving-side terminal, when the communication circuit receives this second frame, it performs the FCS error check on the data of the second frame, and will abandon the second frame when the communication circuit on the receiving-side terminal determines that data is corrupted (NG). Therefore, the host system (reproducing apparatus) on the receiving-side terminal cannot obtain the data stored in the second frame, and cannot reproduce this data. Consequently, dropout of the reproduction data (discontinuity in sound) occurs in the host system. Since the data is abandoned (i.e., the data is not correctly received), the communication circuit in the receiving-side terminal does not produce the frame of ACK.
Thereafter, the transmitting-side terminal transmits the second frame again in response to the fact that it does no receive the ACK from the receiving-side terminal even after standby over a predetermined period. The receiving-side terminal receives the retransmitted second frame, and performs the FCS error check. When it is determined from the error check that there is no error (OK), the communication circuit provides the data of the second frame to the host system side. The host system reproduces a sound from the received data. Thereafter, the communication circuit in the receiving-side terminal will perform the FCS error check on each received frame in a similar manner.
According to FIG. 46, the host system in the receiving-side terminal cannot obtain the received data during a period from the reception (reproduction) of the first data to the reception (reproduction) of the second data so that dropout of the sound occurs to cause discontinuity in sound which gives the user an unpleasant feeling during this period. In data communications requiring a real-time property (real-time response), it is required to overcome the above unpleasant feeling.
However, the host system in the receiving-side terminal may have a function of repairing or correcting corrupt data (second data), and thereby the error correction may restore the data. In this case, no dropout occurs in output (reproduced) sound, and the sound can be reproduced substantially correctly to avoid a trouble interfering with listening by the user.